The invention relates to a shed forming device for a weaving machine, comprising two or more sets of hooks, which are provided with complementary hooks operating in conjunction with a tackle.
This device is more particularly used in two- or more-positions open-shed Jacquard machines.
This invention likewise relates to a weaving machine provided with such a shed forming device or Jacquard machine.
A Jacquard machine, or in a broader sense, a shed forming device, comprises one or more selection systems which are designed to select whether or not one or more hooks. When selected, a hook is taken along by a lifting element, being part of a set of lifting elements consisting of at least two lifting elements moving up and down in opposite phase.
Two or more complementary hooks form a set of hooks. Complementary hooks are hooks operating in conjunction, which by influencing one or more selection elements and which, by using lifting means, may be brought into different positions, so that the warp yarns on a weaving machine may be brought into different positions or at different heights according to the open-shed principle by means of pulley cords and pulley elements.
An important feature of a shed forming device is the footprint of a selection system, which may be defined in the following ways:                the surface taken up by one selection system in a vertical projection of the device on a horizontal plane; or        the product of the pitch in the longitudinal direction and the pitch in the cross direction, the “pitch” being the distance between the center lines of two selection elements situated next to one another.        
Similar shed forming devices are generally known. Thus, in the European patent publication EP 0 188 074 a selection and guiding device for the hooks of an electronically controlled two-position open-shed Jacquard machine is described. The hooks are flexible and made of ferromagnetic material, and the selection element is an electromagnet. The electromagnet is able to bent the hooks to a first position in which the hook is taken along by a blade moving up and down and to a second position, where the hook (when selected) will hook onto a protrusion and therefore will be kept at a stationary height. In this manner a hook may be moved up and down at will or kept at a specific height.
Furthermore a three-position open-shed Jacquard machine is known from the Belgian patent BE 1 009 047, each selection system of which comprises two solenoids situated above one another. These solenoids are designed to act on two hooks operating in conjunction, which were made in two parts. The hooks may be moved up and down by two blade systems operating above one another. This device can be operated as a three-position open-shed Jacquard machine.
From FR 2 648 159 a selection device is known for an open-shed jacquard machine, in which two complementary sets of hooks and two selection elements are needed in order to realize the three positions of the shed.
In DE 29802064 a tackle system for a three-position Jacquard machine is described, in which two control elements have been provided each operating in conjunction with a complementary set of hooks and in which two pulleys, situated above one another, are disposed diagonally and crosswise, because they are each connected crosswise to a hook from each of the two complementary sets of hooks, through a cord running around their upper pulley wheel.
The disadvantage of this device is that, in order to realize the three positions, two controlling elements are required and in order to reach the three positions a pulley of the lower level has to operate in conjunction with a pulley of the upper level.
Similar Jacquard machines may be realized with a footprint of 8×22 mm2, which is rather large. It causes the problem that the number of selection systems per Jacquard machine is rather restricted in this way, and that the dimensions of the Jacquard machine become too large when more selection systems are installed.
The Belgian patent application BE 1 013 193 offers a solution to this problem, in which a shed forming device for a weaving machine is described, comprising a number of combinations of at least to selection systems, with selection elements disposed one above the other respectively, each system comprising two hooks operating in conjunction and movable up and down by means of lifting means, which are selected by a selection element, so that they may be kept at a stationary height and where the hooks of various selection elements of a combination may be moved up and down independently from one another. This device therefore has lifting blades in two pieces moving two sets of hooks. These two sets of hooks are of a different length, so that each set of hooks may be controlled by a separate set of electromagnetic selection systems. Both sets of electromagnetic selection systems are installed above one another.
The problem of such a device is that the number of selection systems per unit of surface is practically doubled, but this provided said lifting blades in two pieces are used. Because of this doubling of the number of selection systems more pulleys are needed, because of which they have, either partly or all together, a smaller bearing diameter and either are installed next to one another and will have bearings with a smaller width or both. Because of this smaller width of the bearing and/or diameter of the pulleys, the life span will be shorter and the capacity as to speed and strength will be influenced in a negative sense.
Further disadvantages of this device are:                lifting elements in two pieces are difficult to manufacture and expensive;        because the blades are situated at two levels, half of the hooks have to be put through the lifting means, which increases the assembly time (and also makes the preassembly more difficult) and likewise will make possible replacements of parts in the Jacquard machine more difficult;        the hooks are divided in two sets of hooks which are considerably different as to length, which requires special provisions for the longest hooks and causes more risks of inaccurate selections, damage and breakage;        the two electromagnetic selection systems arranged above one another are situated in parts of the housing, which are substantially different in thickness, which causes the selection systems to react non-identically on these two levels;        in order to avoid the various tackle cords from getting in touch with one another or impeding one another, special dispositions have to be respected which will complicate assembly and will cause more risks and mistakes during assembly;        such a device requires a substantial installing height because the two sets of selection systems have to be arranged above one another.        